Recent studies suggest that resuscitated hemorrhagic shock leads to an inappropriate or "dysfunctional" increase in the expression of a portfolio of inflammatory mediators, including tumor necrosis factor (TNF), interleukin-1beta (IL-1b), interleukin-6 (IL-6) and nitric oxide (NO), which can in turn provoke a number of deleterious effects in the heart, most notably LV dysfunction. Inflammatory mediators are principal effector proteins of the "innate immune system," a phylogenetically conserved early warning system that enables the host to rapidly discriminate "danger signals" (e.g. ROIs) in the environment. Studies from this and other laboratories have identified the presence of a family of innate immune receptors in the heart termed Toll-like receptors (TLRs). Importantly, these studies have shown that Toll-like receptor mediated signaling activates proinfiammatory mediators in the heart in response to a variety of different forms of environmental stress, including oxidative stress. Our preliminary studies in mice that are deficient in TLR-2 mediated signaling (TLR-2D) show that TLR-2 mice have less reperfusion induced expression of inflammatory mediators and are resistant to the deleterious effects of ischemia-reperfusion injury on LV function. Based upon the foregoing observations the immediate specific objective of this proposal will be to test the following hypotheses: (1) Signaling through Toll-like receptor 2 (TLR-2) amplifies reperfusion-induced expression of inflammatory mediators in the heart through a MyD88/TIRAP dependent pathway, and (2) TLR-2 mediated amplification of inflammatory mediators exaggerates the LV dysfunction that supervenes following resuscitated hemorrhagic shock. These hypotheses will be tested using mutually complementary murine model systems of low-flow ischemia reperfusion (LF-I/R) ex vivo and resuscitated hemorrhagic shock (R-H/S) in vivo. Four Aims are envisioned. In Specific Aim 1 we will test the hypothesis that signaling through TLR-2 amplifies the expression of inflammatory mediators in the heart following LFI/ R injury through a MyD88/TIRAP dependent signaling pathway. Specific Aim 2 will test the hypothesis that TLR-2 mediated signaling exaggerates the left ventricular (LV) dysfunction that occurs following low-flow ischemia/reperfusion LF-I/R through increased expression of inflammatory mediators. In Specific Aim 3, we will test the hypothesis that signaling through TLR-2 amplifies the expression of inflammatory mediators in the heart following resuscitated hemorrhagic shock (R-HS) through a MyD88/TIRAP dependent signaling pathway. Specific Aim 4 will test the hypothesis that TLR-2 mediated signaling exaggerates the left ventricular (LV) dysfunction that occurs following R-HS through increased expression of inflammatory mediators. Taken together, Specific Aims 1-4 should provide definitive new information regarding the mechanisms of activation, as well as the role of the innate immune system in resuscitated hemorrhagic shock.